Method of shielding furnace tubes



Mgrch 23, 1965 REAGAN 3,174,463

METHOD OF SHIELDING FURNACE TUBES Filed NOV. 1, 1962 FIG.

INVENTOR.

JOHN J. REAGAN ATTORNEYS n te S es P t n 3,174,463 METHOD OF SHIELDING FURNACE TUBES John J. Reagan, Parma, Ohio, assignor to The Standard Oil Company, Cleveland, Ohio, a corporation of Ohio 7 Filed Nov. 1, 1962, Ser. No. 234,656

2 Claims. (Cl. 1224) This invention relates in general to furnaces of the type in widespread use, for example, in the petroleum industry and relates more particularly to a novel method for temporarily shielding a furnace tube hot spot to prevent tube failure on such account. The term hot spot of course refers to a relatively small area or spot on a tube where the temperature has increased abnormally due to conduitions existing within the tube. This heat buildup, if not detected and stopped, can eventually cause tube failure and consequent unplanned shutdown of the furnace.

The above-described heat buildup is generally caused by a gradual, localized accumulation of coke on the inside wall of the tube. The coke forms an insulating layer which inhibits the heat transfer through the wall of the tube to the fluid flowing therethrough, the heat being generated by a suitable burner assembly within the lower portion of the furnace. As the heat transfer is thus inhibited and the temperature of the tube wall increases, more coke is formed and the tube will eventually begin to glow, with ultimate failure if the progressive deterioration is not checked. Metal is lost at the spots by scaling and flaking and there is of course significant strength loss.

With the above in mind, it is a primary object of the invention to form a tube shield adapted to be positioned adjacent the hot spot on the tube for temporarily arresting the above-described cycle by shielding the hot spot from the heat source.

It is a still further object of the invention to form a tube shie'ld adapted for use with existing furnace structures of varying types, the only requirement being that the furnace be provided with the usual peep holes, explosion doors or similar openings in the side walls thereof.

Other objects and advantages of the present invention will become apparent as the following description proceeds.

To the accomplishment of the foregoing and related ends, the invention, then, comprises the features hereinafter fully described and particularly pointed out in the claims, the following description and the annexed drawings setting forth in detail certain illustrative embodiments of the invention, these being indicative, however, of but a few of the various ways in which the principle of the invention may be employed.

In said annexed drawings:

FIG. 1 is a perspective view of a vertical tube furnace, the wall of the furnace being broken away to show the vertical heater tubes and the novel tube shielding means of the invention;

FIG. 2 is an enlarged, vertical cross-sectional view taken through the furnace wall and more clearly shows the positioning of the tube shield adjacent the tube;

FIG. 3 is an enlarged view of the shield body.

Referring now to the drawings in detail, wherein like reference characters are used to designate like parts, a vertical tube furnace is shown generally at and is of a well-known and conventionally employed type, comprising an outer cylindrical metal shell 12 having disposed therewithin a refractory lining 14 capable of sustaining the relatively high temperatures occurring within the furnace. A conventional gas burner assembly is provided and comprises a plurality of spaced individual burners 16 which communicate at their upper ends with the bottom of the furnace. These burners 16 serve to 3,174,463 .Patented Mar. 23, 1965 heat a plurality of vertically extending circumferentially spaced tubes 18 supported by any suitable means adjacent, but preferably out of contact with, the lining 14. The radiant heat from the burners serves to heat the fluid, which might be, for example, crude oil, flowing upwardly through the tubes 18 from a bottom header 20. The furnace is supported above the ground by any suitable support means, indicated at 22. circumferentially spaced openings 23, only one of which is shown in FIG. 1, are provided through the furnace wall for permitting visualinspection of the furnace interior during operation. Referring to FIG. 2, a peep hole 24 is provided in the form of an opening in door 25, such opening being covered, if desired, by means of a pivotally mounted closure plate 26. As illustrated, the door 25 is hinged at the upper end thereof and can be latched at the lower end thereof. The furnace structure thus far described is well known and further details thereof are not deemed necessary for a complete understanding of the tube shielding means which comprises the present invention.

As set forth above,there often occurs during normal operation of the furnace a localized hot spot resulting from a cyclical coke buildup on the interior wall of a tube 18 and the corresponding temperature increase of the tube in the area of the hotspot due to the reduced heat exchange. Since this temperature increase is somewhat gradual, it cannot initially be ascertained through the usual periodic inspection of the furnace interior through the peep holes 24. However, as the tube wall temperature at the localized hot spot continues to increase, the tube will start to glow, such glowing of course being readily detected by observation through the peep holes.

The assembly of the invention for shielding such a hot spot is generally indicated at 27 and, referring to FIGS. 2 and 3, comprises a rod member 28 and a curved plate member 30, the latter being secured to the rod 28 by any suitable means, e.g., welding. The rod 28 and plate 30 are preferably made of a heat resistant steel alloy, e.g., stainless steel, possessing suflicient flexibility to enable the rod portion 28 to be bent to the desired shape and the plate portion 30 to be rolled to a curved shape approximating the curvature of the tube 18. The dimensions of the plate 30 are, of course, sufficient to satisfactorily cover the hot spot on the tube and thereby shield the same from the radiant heat.

If, during normal operation and inspection of the furnace, a hot spot is detected by visual observation through the peep holes 24, the distance and direction of the hot spot from preferably the most adjacent peep hole is determined as closely as possible. The rod 28, which is normally straight is then bent to span, in the most convenient path, the distance from the adjacent peep hole 24 to the hot spot.

The rod 28, is for example, t-hus bent to provide a generally vertical end pontion 28a carrying a plate 30 and a partially horizontal opposite end portion 28b which extends outwardly of the furnace through the opening 23. The door 25 is of course unlatohed to allow the end portion 28b to extend outwardly of the furnace through the opening. The remainder of the opening is preferably sealed with any suitable material, e.g., insulating paste, in order to maintain efficient operation of the furnace. The end portion 28b also provides a convenient means for swinging the entire shield assembly into position.

The installation of the shield assembly is accomplished in a very simple manner and while the furnace is in operation, the latter feature being of obvious importance. The shield assembly, with the plate end first, is inserted through the adjacent peep hole. The assembly is then swung through manipulation of the rod end 28b to dispose the plate 30 adjacent to and preferably in contact with the tube wall overlying the hot spot. It will be obvious that the transverse dimension of the plate 30 must be less than at least one dimension of the peep hole in order to accommodate such insertion. The end 28b is then secured in place by any suitable securing means. As shown in FIG 2, the securing of the shielding assembly in the form shown is in the form of a tack weld 32, the bottom of the end 28b of the rod being welded to the exterior shell of the furnace. Before end 28b is welded, the rod 28, through such end 281) Will-be manipulated to exert a pressure on the plate 30 for maintaining the same in contact with the tube wall. As will be evident, any suitable means in addition to that shown can be employed for maintaining the shielding assembly in place. In addition to the vertical stability provided by the tack weld, the generally similar curvature of the plate 30 and the tube wall provides a horizontal stability to the shield assembly after same has been secured imposition.

The entire installation takes only a few minutes and is effective immediately to arrestthe temperature buildup at the hot spot in the tube wall. The shield assembly can then be retained in place until the reaching of a planned shutdown date, at which time the shielding assembly can be removed and the damaged tube can be replaced or repaired.

Although in the drawing we have shown but a single shield assembly associated with a particular heater'tube, this illustration is by way of example only and it should be understood that damaged tubes other than the one shown can be shielded in the same manner, with the bent shape of rod 28 varying, of course, for each installation, such bent shape depending on the location of the tube and the hot spot formed therein. It is also possible to have more than one such shield assembly installed at any time if more than one hot spot is observed before the planned shutdown date is reached. There are a plurality of peep hole-s available if such a condition arises. Further, although peep holes have been employed in the form shown for insertion of the shielding means into the furnace interior, it will be obvious that other furnace wall openings, such as, for example, explosion doors, could also be satisfactorily employed. It is also envisioned that in certain types of furnaces other than the form disclosed herein, e.g., in box type furnaces, it may be necessary to cut a hole in the furnace wall adjacent the hot spot to provide for the shield insertion.

Other modes of applying the principle of the invention may be employed, change being made as regards the details described, provided the features stated in any of the following claims or the equivalent of such be employed.

I, therefore, particularly point out and distinctly claim as my invention:

1. The method of protecting normally unshielded furnace heat exchange tubes from the effects of localized areas of abnormal temperature increase, without interruption of operation of the furnace, which comprises the steps of visually inspecting the heat exchange tubes to locate a localized hot spot on the unshielded heater tu be, forming an elongated heat resistant support capable of extending from a selected available opening in the wall of the furnace to a noted high temperature area on one of the tubes, attaching a heat resisting body to the intended inner end of said support, with said body being of a shape and size as to pass through the wall opening, placing the body immediately adjacent the tube over the high temperature area on the tube through insertion and manipulation of the support from the exterior of the furnace, and securing the exterior portion of the support to maintain the body in such position.

2. The method of protecting normally unshielded heat exchange tubes in a furnace from the effects of localized areas of abnormal temperature increase, without interruption of operation of the furnace, which comprises the steps of visually inspecting the heat exchange tubes to locate localized hot spots on the tubes, forming an elongated shield assembly capable of extending from a selected available opening in the wall of the furnace to a noted high temperature area on one of the tubes, placing a part of the shield assembly over the high temperature area through insertion and manipulation of the shield assembly from the exterior of the furnace, and securing the exterior portion of the shield assembly to maintain the same in such position.

References Cited in the file of this patent UNITED STATES PATENTS Re. 24,857 Wasp Aug. 9, 1960 

2. THE METHOD OF PROTECTING NORMALLY UNSHIELDED HEAT EXCHANGE TUBES IN A FURNACE FROM THE EFFECTS OF LOCALIZED AREAS OF ABNORMAL TEMPERATURE INCREASE, WITHOUT INTERRUPTION OF OPERATION OF THE FURNACE, WHICH COMPRISES THE STEPS OF VISUALLY INSPECTING THE HEAT EXCHANGE TUBES TO LOCATE LOCALIZED HOT SPOTS ON THE TUBES, FORMING AN ELONGATED SHIELD ASSEMBLY CAPABLE OF EXTENDING FROM A SELECTED AVAILABLE OPENING IN THE WALL OF THE FURNACE TO A NOTED HIGH TEMPERATURE AREA ON ONE OF THE TUBES, PLACING A PART OF THE SHIELD ASSEMBLY OVER THE HIGH TEMPERATURE AREAS THROUGH INSERTION AND MANIPULATION OF TH SHIELD ASSEMBLY FROM THE EXTERIOR OF THE FURNACE, AND SECURING THE EXTERIOR PORTION OF THE SHIELD ASSEMBLY TO MAINTAIN THE SAME IN SUCH POSITION. 